For decades, the presence or absence of lexical tone has been considered a sufficient test to classify Northern and Southern Qiang languages (H. Sun 1981). No Northern Qiang (NQ) dialect had been described with morphemic tone, and no Southern Qiang (SQ) dialect had been described without morphemic tone (although there has been some debate about the Puxi variety, cf. Huang 2004). Similarly, Northern Qiang dialects have been described with distinctive vowel length, while this is not found in SQ. 

Beginning with the authors' initial contact with the Yunlinsi dialect of Northern Qiang in 2005, there have appeared tantalizing minimal pairs which seem to be distinguished by tone. It appears that tone might only distinguish long vowels, as in the following examples (minimal triples are scarce):

Thus far, all examples of words that appear to carry a tone distinction are monosyllables, and vowel length appears to be involved in some way. This paper reports on the results of speech synthesis and perception tests performed onsite in the Summer of 2013 to determine whether at least some morphemes in Yunlinsi are specified for pitch, which has been proposed as a definition of a tone language (Hyman 2001:1368). The study also intends to discover whether short vowels can carry tonal distinctions, as well as what happens to tonal distinctions in a larger morphosyntactic context.

References.

Huang, Chenglong. 2004. A reference grammar of the Puxi variety of Qiang. Hong Kong: CUHK dissertation.

Hyman, Larry. 2001. Tone systems. In Haspelmath, Martin, et al., eds. Language typology and language universals: an international handbook. Berlin & New York: Walter de Gruyter. vol. 2:1367-1380.

Sun, Hongkai. 1981a. Qiangyu Jianzhi [A Brief Description of the Qiang Language]. Beijing: Nationalities Press. (in Chinese)